Solution-processed thin film transistors hold great promise to fundamentally change the semiconductor industry. Their uses run the gamut of conventional transistor uses, and may be formed into light emitting structures. Materials used in the thin films, such as conductive polymers, are durable and can be flexible, thereby providing a range of uses in demanding environments.
The solution-processed thin film transistors also hold the potential to be fabricated by simple techniques, e.g., direct printing of circuits. A long-term goal is to have circuits of solution-processed thin film transistors printed on a substrate in similar fashion to the way ink is patterned in a printing press. Proposed manufacturing techniques seek to employ relatively simple procedures such as inkjet printing. A critical issue, however, remains feature size. Small feature sizes, e.g., small channel lengths, produce small threshold voltages and fast operation. However, introducing conventional techniques to produce small feature sizes, e.g., lithography, adds complexity and expense that contradicts the goal of achieving simply manufactured devices and circuits.
Solution-processed deposition also places demands on the materials used to form features, particularly when an ink jet deposition process is utilized. The material being deposited must have adhesion, temperature, and other material characteristics suitable for deposit through an ink jet head. On the other hand, the material deposited should quickly achieve solid phase, adhere to the substrate or material layers onto which it is deposited, and remain within the boundaries intended by the controlled ink jet deposition.
Screen printing is an example technique for patterning drain and source regions of solution-processed thin film transistors. A gap of about 100 μm may be produced by this technique. Other techniques may produce smaller sized gaps, but have limitations such as being limited to use on small substrates. An example is a technique that converts portions of organic polymer materials to dielectric through selective use of UV radiation. Thus, there remains a need for solution-processed thin film formation methods capable of producing small feature sizes.